I'm running the Pro version 2.12.1. I am only using Google calendar with a number of additional subscribed Google calendars (country hollidays).
I can see them in Google web version but not in Rainlendar.
Since the only asked info is the gmail address what can I do to include those additional calendars.

When you add a new Google calendar (v3) to Rainlendar you enter the email address and click the "Select calendar" button. This opens the authentication dialog. After you grant Rainlendar the access to your Google account Rainlendar will download the calendar list and you can choose one of them from the drop down control.